1. Field of the Invention
The present invention relates to an all-solid lithium ion secondary battery including no organic substance.
2. Related Art
An all-solid lithium ion secondary battery in which a solid electrolyte layer and an electrode layer are configured using an inorganic solid and not using an organic substance has been expected as a safe battery. The reason is that this battery is free from any problems concerning leakage of an organic electrolytic solution and generation of gas from the organic electrolytic solution. Further, the all-solid lithium ion secondary battery is less likely to produce a side reaction other than battery reactions as compared to liquid batteries, and therefore can be expected to have a long operating life as compared to the liquid batteries. Especially, an all-solid lithium ion secondary battery that does not use a sulfide having a possibility of generating poisonous gas exhibits high safety.
One example of the all-solid lithium ion secondary battery includes one in which a positive electrode layer and a negative electrode layer are laminated and sintered respectively on both sides of a solid electrolyte layer. In the all-solid lithium ion secondary battery, it is possible that constituent particles present between respective layers and in each thereof are physically bonded together by sintering. However, during sintering, at a sintering interface between an electrode active material and a solid electrolyte, an inactive material that is neither the electrode active material nor the solid electrolyte is generated, resulting thereby in a problem that ion conductivity resistance increases and a problem that the amount of the electrode active material contributing to charge-discharge decreases.
In the production of an all-solid lithium ion secondary battery, for reduced production cost, it has been expected to co-sinter a positive electrode layer, a solid electrolyte layer and a negative electrode layer to bond these layers together. When the positive electrode layer, the solid electrolyte layer and the negative electrode layer are co-sintered, it is specifically difficult to solve the aforementioned problems. The reason is that it is necessary to inhibit, under one kind of sintering condition, generation of an inactive material due to interface reaction at two types of interfaces that are a positive electrode active material-solid electrolyte interface and a negative electrode active material-solid electrolyte interface. For example, even when a sintering condition for inhibiting generation of an inactive material is applied in the negative electrode active material-solid electrolyte interface, this sintering condition is frequently unsuitable for sintering the positive electrode active material-solid electrolyte interface.
In Patent Document 1, an electrode active material and a solid electrolyte common in a polyanion are combined and also the same material is used as electrode active materials of a positive electrode and a negative electrode, whereby the aforementioned problems are solved and then the interface resistance of the solid electrolyte and the electrode active material after sintering is reduced.
[Patent Document 1] Japanese Unexamined Patent Application, Publication No. 2009-140910